Dehydrocyclization with an acidic multimetallic catalytic composite

ABSTRACT

Dehydrocyclizable hydrocarbons are converted to aromatics by contacting them at dehydrocyclization conditions with an acidic multimetallic catalytic composite comprising a combination of catalytically effective amounts of a platinum group component, a bismuth component, a cobalt component, and a halogen component with a porous carrier material. The platinum group, bismuth, cobalt and halogen components are present in the multimetallic catalyst in amounts respectively, calculated on an elemental basis, corresponding to about 0.01 to about 2 wt. % platinum group metal, about 0.05 to about 5 wt. % cobalt, about 0.01 to about 5 wt. % bismuth, and about 0.1 to about 3.5 wt. % halogen. Moreover, the catalytically active sites induced by these metallic components are uniformly dispersed throughout the porous carrier material and these metallic components are present in the catalyst in carefully controlled oxidation states such that substantially all of the platinum group component is in the elemental metallic state, substantially all of the bismuth component is preferably in an oxidation state above that of the elemental metal, and substantially all of the catalytically available cobalt component is present in the elemental metallic state or in a state which is reducible to the elemental metallic state under dehydrocyclization conditions, or in a mixture of these states. A specific example of dehydrocyclization method disclosed herein is a method for converting a feed mixture of n-hexane and n-heptane to a product mixture of benzene and toluene which involves contacting the feed mixture and a hydrogen stream with the acidic multimetallic catalyst disclosed herein at dehydrocyclization conditions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of my prior, copendingapplication Ser. No. 602,935 filed Aug. 8, 1975 (now U.S. Pat. No.3,981,795). All of the teachings of this prior application arespecifically incorporated herein by reference.

The subject of the present invention is, broadly, an improved method fordehydrocyclizing a dehydrocyclizable hydrocarbon to produce an aromatichydrocarbon. In a narrower aspect, the present invention involves amethod of dehydrocyclizing aliphatic hydrocarbons containing 6 to 20carbon atoms per molecule to monocyclic aromatic hydrocarbons withminimum production of side products such as C₁ to C₅ hydrocarbons,bicyclic aromatics, olefins and coke. In another aspect, the presentinvention relates to the dehydrocyclization use of an acidicmultimetallic catalytic composite comprising a combination ofcatalytically effective amounts of a platinum group component, a cobaltcomponent, a bismuth component, and a halogen component with a porouscarrier material. This acidic multimetallic composite has been found topossess highly beneficial characteristics of activity, selectivity, andstability when it is employed in the dehydrocyclization ofdehydrocyclizable hydrocarbons to make aromatics such as benzene,toluene and xylene.

The conception of the present information followed from my search for anovel catalytic composite possessing a hydrogenation-dehydrogenationfunction, a controllable cracking and isomerization function, andsuperior conversion, selectivity, and stability characteristics whenemployed in hydrocarbon conversion processes that have traditionallyutilized dual-function catalytic composites. In my prior application, Idisclosed a significant finding with respect to a multimetalliccatalytic composite meeting these requirements. More specifically, Idetermined that a combination of specified amounts of a cobalt componentand a bismuth component can be utilized, under certain conditions, tobeneficially interact with the platinum group component of adual-function acidic catalyst with a resultant marked improvement in theperformance of such a catalyst. Now I have ascertained that an acidicmultimetallic catalytic composite, comprising a combination ofcatalytically effective amounts of a platinum group component, a cobaltcomponent, a bismuth component and a halogen component with a porouscarrier material, can have superior activity, selectivity, and stabilitycharacteristics when it is employed in a ring-closure ordehydrocyclization process if the catalytically active sites induced bythese components are uniformly dispersed in the porous carrier materialin the amounts specified hereinafter and if the oxidation state of theactive metallic ingredients are carefully controlled so thatsubstantially all of the platinum group component is present in theelemental metallic state, substantially all of the bismuth component ispresent in an oxidation state above that of the elemental metal, andsubstantially all of the catalytically available cobalt component ispresent in the elemental metallic state or in a state which is reducibleto the elemental metallic state under dehydrocyclization conditions orin a mixture of these states.

The dehydrocyclization of dehydrocyclizable hydrocarbons is an importantcommercial process because of the great and expending demand foraromatic hydrocarbons for use in the manufacture of various chemicalproducts such as synthetic fibers, insecticides, adhesives, detergents,plastics, synthetic rubber, pharmaceutical products, high octanegasoline, perfumes, drying oils, ion-exchange resins, and various otherproducts well known to those skilled in the art. One example of thisdemand is in the manufacture of alkylated aromatics such asethylbenzene, cumene and dodecylbenzene by using the appropriatemono-olefins to alkylate benzene. Another example of this demand is inthe area of chlorination of benzene to give chlorobenzene which is thenused to prepare phenol by hydrolysis with sodium hydroxide. The chiefuse for phenol is of course in the manufacture of phenol-formaldehyderesins and plastics. Another route to phenol uses cumene as a startingmaterial and involves the oxidation of cumene by air to cumenehydroperoxide which can then be decomposed to phenol and acetone by theaction of an appropriate acid. The demand for ethylbenzene is primarilyderived from its use to manufacture styrene by selectivedehydrogenation; styrene is in turn used to make styrene-butadienerubber and polystyrene. Ortho-xylene is typically oxidized to phthalicanhydride by reaction in vapor phase with air in the presence of avanadium pentoxide catalyst. Phthalic anhydride is in turn used forproduction of plasticizers, polyesters and resins. The demand forpara-xylene is caused primarily by its use in the manufacture ofterephthalic acid or dimethyl terephthalate which in turn is reactedwith ethylene glycol and polymerized to yield polyester fibers.Substantial demand for benzene also is associated with its use toproduce aniline, Nylon, maleic anhydride, solvents and the likepetrochemical products. Toluene, on the other hand, is not, at leastrelative to benzene and the C₈ aromatics, in great demand in thepetrochemical industry as a basic building block chemical; consequently,substantial quantities of toluene are hydrodealkylated to benzene ordisproportionated to benzene and xylene. Another use for toluene isassociated with the transalkylation of trimethylbenzene with toluene toyield xylene.

Responsive to this demand for these aromatic products, the art hasdeveloped a number of alternative methods to produce them in commercialquantities. One method that has been widely studied involves theselective dehydrocyclization of a dehydrocyclizable hydrocarbon bycontacting the hydrocarbon with a suitable catalyst atdehydrocyclization conditions. As is the case with most catalyticprocedures, the principal measure of effectiveness for thisdehydrocyclization method involves the ability to perform its intendedfunction with minimum interference of side reactions for extendedperiods of time. Th analytical terms used in the art to broadly measurehow well a particular catalyst performs its intended functions in aparticular hydrocarbon conversion reaction are activity, selectivity,and stability, and for purposes of discussion here, these terms aregenerally defined for a given reactant as follows: (1) activity is ameasure of the catalyst's ability to convert the hydrocarbon reactantinto products at a specified severity level where severity level meansthe specific reaction conditions used -- that is, the temperature,pressure, contact time, and presence of diluents such as H₂ ; (2)selectivity usually refers to the amount of desired product or productsobtained relative to the amount of the reactant charged or converted;(3) stability refers to the rate of change with time of the activity andselectivity parameters -- obviously the smaller rate implying the morestable catalyst. More specifically, in a dehydrocyclization process,activity commonly refers to the amount of conversion that takes placefor a given dehydrocyclizable hydrocarbon at a specified severity leveland is typically measured on the basis of disappearance of thedehydrocyclizable hydrocarbon; selectivity is typically measured by theamount, calculated on a weight percent of feed basis or on a molepresent of converted dehydrocyclizable hydrocarbon basis, of the desiredaromatic hydrocarbon or hydrocarbons obtained at the particular activityor severity level; and stability is typically equated to the rate ofchange with time of activity as measured by disappearance of thedehydrocyclizable hydrocarbon and of selectivity as measured by theamount of desired aromatic hydrocarbon produced. Accordingly, the majorproblem facing workers in the hydrocarbon dehydrocyclization orring-closure art is the development of a more active and selectivecatalytic composite that has good stability characteristics.

I have now found a dual-function acidic multimetallic catalyticcomposite which possesses improved activity, selectivity, and stabilitywhen it is employed in a process for the dehydrocyclization ofdehydrocyclizable hydrocarbons. In particular, I have determined thatthe use of an acidic multimetallic catalyst, comprising a combination ofcatalytically effective amounts of a platinum group component, a cobaltcomponent, a bismuth component, and a halogen component with a porousrefractory carrier material, can enable the performance of adehydrocyclization process to be substantially improved if thecatalytically active sites induced by the metallic components areuniformly dispersed throughout the carrier material in the amounts andrelative relationships specified hereinafter and if their oxidationstates of the active metallic ingredients are carefully controlled to bein the states hereinafer specified. Moreover, particularly good resultsare obtained when this catalyst is prepared and maintained, during usein the dehydocyclization method, in a substantially sulfur-free state.This acidic multimetallic catalytic composite is particularly useful inthe dehydrocyclization of C₆ to C₁₀ paraffins to produce aromatichydrocarbons such as benzene, toluene, and the xylenes with minimizationof by-products such as C₁ to C₅ saturated hydrocarbons, bicyclicaromatics, olefins and coke.

In sum, the current invention involves the significant finding that acombination of a cobalt component and a bismuth component can beutilized under the circumstances specified herein to beneficiallyinteract with and promote an acidic dehydrocyclization catalystcontaining a platinum group metal when it is used in the production ofaromatics by ring-closure of aliphatic hydrocarbons.

It is, accordingly, one object of the present invention to provide anovel method for the dehydrocyclization of dehydrocyclizablehydrocarbons utilizing an acidic multimetallic catalytic compositecomprising catalytically effective amounts of a platinum groupcomponent, a cobalt component, a bismuth component and a halogencomponent combined with a porous carrier material. A second object is toprovide a novel acidic catalytic composite having superior performancecharacteristics when utilized in a dehydrocyclization process. Anotherobject is to provide an improved method for the dehydrocyclization ofparaffin hydrocarbons to produce aromatic hydrocarbons which methodminimizes undesirable by-products such as C₁ to C₅ saturatedhydrocarbons, bicyclic aromatics, olefins and coke.

In brief summary, one embodiment of the present invention involves amethod for dehydrocyclizing a dehydrocyclizable hydrocarbon whichcomprises contacting the hydrocarbon at dehydrocyclization conditionswith an acidic multimetallic catalytic composite comprising porouscarrier material containing a uniform dispersion of catalyticallyeffective amounts of a platinum group component, a cobalt component, abismuth component, and a halogen component. Moreover, substantially allof the platinum group component is present in the composite in theelemental metallic state, subtantially all of the bismuth component ispreferably present in a positive oxidation state, and substantially allof the catalytically available cobalt component is present in theelemental metallic state or in a state which is reducible to theelemental metallic state under dehydrocyclization conditions or in amixture of these states. Further these components are present in thiscomposite in amounts, calculated on an elemental basis, sufficient toresult in the composite containing about 0.01 to about 2 wt. % platinumgroup metal, about 0.05 to about 5 wt. % cobalt, about 0.01 to about 5wt. % bismuth and about 0.1 to about 3.5 wt. % halogen.

A second embodiment relates to the dehydrocyclization method describedin the first embodiment wherein the dehydrocyclizable hydrocarbon is analiphatic hydrocarbon containing 6 to 20 carbon atoms per molecule.

A highly preferred embodiment comprehends the dehydrocyclization methodcharacterized in the first embodiment wherein the catalyst is preparedand maintained in a sulfur-free state and wherein the contacting isperformed in a substantially sulfur-free environment.

Another embodiment relates to the catalytic composite used in the first,second or third embodiments and involves the further limitation that thehalogen component is combined chloride.

Other objects and embodiments of the present invention involve specificdetails regarding essential and preferred catalytic ingredients,preferred amounts of ingredients, suitable methods of multimetalliccomposite preparation, suitable dehydrocyclizable hydrocarbons,operating conditions for use in the dehydrocyclization process, and thelike particulars. These are hereinafter given in the following detaileddiscussion of each of these facets of the present invention.

Regarding the dehydrocyclizable hydrocarbon that is subjected to themethod of the present invention, it can in general be any aliphatichydrocarbon or substituted aliphatic hydrocarbon capable of undergoingring-closure to produce an aromatic hydrocarbon. That is, it is intendedto include within the scope of the present invention, thedehydrocyclization of any organic compound capable of undergoingring-closure to produce an aromatic hydrocarbon containing the same, orless than the same, number of carbon atoms than the reactant compoundand capable of being vaporized at the dehydrocyclization temperaturesused herein. More particularly, suitable dehydrocyclizable hydrocarbonsare: aliphatic hydrocarbons containing 6 to 20 carbon atoms per moleculesuch as C₆ to C₂₀ paraffins, C₆ to C₂₀ olefins and C₆ to C₂₀polyolefins. Specific examples of suitable dehydrocyclizablehydrocarbons are: (1) paraffins such as n-hexane, 2-methylpentane,3-methylpentane, 2,2-dimethylbutane, n-heptane, 2-methylhexane,3-ethylpentane, 2,2-dimethylpentane, n-octane, 2-methylheptane,3-ethylhexane, 2,2-dimethylhexane, 2-methyl-3-ethyl-pentane,2,2,3-trimethylpentane, n-nonane, 2-methyloctane, 2,2-dimethyl-heptane,n-decane and the like compounds; (2) olefins such as 1-hexene,2-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene and the likecompounds; and, (3) diolefins such as 1,5-hexadiene,2-methyl-2,4-hexadiene, 2,6-octadiene and the like diolefins.

In a preferred embodiment, the dehydrocyclizable hydrocarbon is aparaffin hydrocarbon having about 6 to 10 carbon atoms per molecule. Forexample, paraffin hydrocarbons containing about 6 to 8 carbon atoms permolecule are dehydrocyclized by the subject method to produce thecorresponding aromatic hydrocarbon. It is to be understood that thespecific dehydrocyclizable hydrocarbons mentioned above can be chargedto the present method individually, in admixture with one or more of theother dehydrocyclizable hydrocarbons, or in admixture with otherhydrocarbons such as naphthenes, aromatics, C₁ to C₅ paraffins and thelike. Thus mixed hydrocarbon fractions, containing significantquantities of dehyrocyclizable hydrocarbons that are commonly availablein a typical refinery, are suitable charge stocks for the instantmethod; for example, highly paraffinic straight run naphthas, paraffinicraffinates from aromatic extraction or adsorption, C₆ to C₉paraffin-rich streams and the like refinery streams. An especiallypreferred embodiment involves a charge stock which is a paraffin-richnaphtha fraction boiling in the range of about 140° to about 400° F.Generally, best results are obtained with a charge stock comprising amixture of C₆ to C₉ paraffins, and especially C₆ to C₉ normal paraffins.

The acidic multimetallic catalyst used in the present dehydrocyclizationmethod comprises a porous carrier material having combined therewithcatalytically effective amounts of a platinum group component, a cobaltcomponent, a bismuth component, and a halogen component.

Considering first the porous carrier material utilized in the presentinvention, it is preferred that the material be a porous, adsorptive,high-surface area support having a surface area of about 25 to about 500m² /g. The porous carrier material should be relatively refractory tothe conditions utilized in the hydrocarbon conversion process, and it isintended to include within the scope of the present invention carriermaterials which have traditionally been utilized in dual-functionhydrocarbon conversion catalysts such as: (1) activated carbon, coke, orcharcoal; (2) silica or silica gel, silicon carbide, clays, andsilicates including those synthetically prepared and naturallyoccurring, which may or may not be acid treated for example, attapulgusclay, china clay, diatomaceous earth, fuller's earth, kaolin,kieselguhr, etc.; (3) ceramics, porcelain, crushed firebrick, bauxite;(4) refractory inorganic oxides such as alumina, titanium dioxide,zirconium dioxide, chromium oxide, beryllium oxide, vanadium oxide,cesium oxide, hafnium, oxide, zinc oxide, magnesia, boria, thoria,silica-alumina, silica-magnesia, chromia-alumina, alumina-boria,silica-zirconia, etc.; (5) crystalline zeolitic alumino-silicates suchas naturally occurring or synthetically prepared mordenite and/orfaujasite, either in the hydrogen form or in a form which has beentreated with multivalent cations; (6) spinels such as MgAl₂ O₄, FeAl₂O₄, ZnAl₂ O₄, MnAl₂ O₄, CaAl₂ O₄, and other like compounds having theformula MO.sup.. Al₂ O₃ where M is a metal having a valence of 2; and(7) combinations of elements from one or more of these groups. Thepreferred porous carrier materials for use in the present invention arerefractory inorganic oxides, with best results obtained with an aluminacarrier material. Suitable alumina materials are the crystallinealuminas known as gamma-, eta, and theta-alumina, with gamma- oreta-alumina giving best results. In addition, in some embodiments thealumina carrier material may contain minor proportions of other wellknown refractory inorganic oxides such as silica, zirconia, magnesia,etc.; however, the preferred support is substantially pure gamma- oreta-alumina. Preferred carrier materials have an apparent bulk densityof about 0.3 to about 0.8 g/cc and surface area characteristics suchthat the average pore diameter is about 20 to 300 Angstroms, the porevolume is about 0.1 to about 1 cc/g and the surface area is about 100 toabout 500 m² /g. In general, best results are typically obtained with agamma-alumina carrier material which is used in the form of sphericalparticles having: a relatively small diameter (i.e. typically about 1/16inch), an apparent bulk density of about 0.3 to about 0.8 g/cc, a porevolume of about 0.4 ml/g, and a surface area of about 150 to about 250m² /g.

The preferred alumina carrier material may be prepared in any suitablemanner and may be synthetically prepared or natural occurring. Whatevertype of alumina is employed, it may be activated prior to use by one ormore treatments including drying, calcination, steaming, etc., and itmay be in a form as activated alumina, activated alumina of commerce,porous alumina, alumina gel, etc. For example, the alumina carrier maybe prepared by adding a suitable alkaline reagent, such as ammoniumhydroxide, to a salt of aluminum such as aluminum chloride, aluminumnitrate, etc., in an amount to form an aluminum hydroxide gel which upondrying and calcining is converted to alumina. The alumina carrier may beformed in any desired shaped such as spheres, pills, cakes, extrudates,powders, granules, tablets, etc., and utilized in any desired size. Forthe purpose of the present invention a particularly preferred form ofalumina is the sphere, and alumina spheres may be continuouslymanufactured by the well-known oil drop method which comprises: formingan alumina hydrosol by any of the techniques taught in the art andpreferably by reacting aluminum metal with hydrochloric acid, combiningthe resultant hydrosol with a suitable gelling agent and dropping theresultant mixture into an oil bath maintained at elevated temperatures.The droplets of the mixture remain in the oil bath until they set andform hydrogel spheres. The spheres are than continuously withdrawn fromthe oil bath and typically subjected to specific aging treatments in oiland an ammoniacal solution to further improve their physicalcharacteristics. The resulting aged and gelled particles are then washedand dried at a relatively low temperature of about 300° F. to about 400°F. and subjected to a calcination procedure at a temperature of about850° F. to about 1300° F. for a period of about 1 to about 20 hours.This treatment effects conversion of the alumina hydrogel to thecorresponding crystalline gamma-alumina. See the teachings of U.S. Pat.No. 2,620,314 for additional details.

The expression "catalytically available cobalt" as used herein isintended to mean the portion of the cobalt component of the subjectcatalytic composite that is available for use in accelerating thedehydrocyclization reaction of interest. For purposes of the presentinvention, it is highly preferred that the catalytically availablecobalt comprise at least about 10% of the total cobalt content of thecatalyst and, even more preferably, at least about 50% thereof. Forcertain types of carrier materials which can be used in the preparationof the instant catalyst composite, it has been observed that a portionof the cobalt incorporated therein is essentially bound-up in thecrystal structure thereof in a manner which essentially makes itcatalytically unavailable; in fact, it is more a part of the refractorycarrier material than a catalytically active component. Specificexamples of this effect are observed when the carrier material can forma refractory spinel or spinel-like structure with a portion of thecobalt component and/or when a refractory cobalt oxide or aluminate isformed by reaction of the carrier material (or precursors thereof) witha portion of the cobalt component. When this effect occurs, it is onlywith great difficulty that the portion of the cobalt bound-up with thesupport can be reduced to a catalytically active state and theconditions required to do this are beyond the severity levels normallyassociated with hydrocarbon conversion conditions and are in fact likelyto seriously damage the necessary porous characteristics of the support.In the cases where cobalt can interact with the crystal structure of thesupport to render a portion thereof catalytically unavailable, theconcept of the present invention merely requires that the amount ofcobalt added to the subject catalyst be adjusted to satisfy therequirements of the support as well as the catalytically availablecobalt requirements of the present invention. Against this background,then, the hereinafter stated specifications for oxidation state anddispersion of the cobalt component are to be interpreted as directed toa description of the catalytically available cobalt. On the other hand,the specifications for the amount of cobalt used are to be interpretedto include all of the cobalt contained in the catalyst in any form.

One essential constituent of the acidic multimetallic catalyst used inthe present invention is a bismuth component. This component may ingeneral be present in the instant catalytic composite in anycatalytically active form such as the elemental metal, a compound likethe oxide, hydroxide, halide, oxyhalide, aluminate, or in chemicalcombination with one or more of the other ingredients of the catalyst.Although it is not intended to restrict the present invention by thisexplanation, it is believed that best results are obtained when thebismuth component is present in the composite in a form whereinsubstantially all of the bismuth moiety is in an oxidation state abovethat of the elemental metal such as in the form of bismuth oxide orbismuth aluminate or a mixture thereof and the subsequently describedoxidation and reduction steps that are preferably used in thepreparation of the instant catalytic composite are specifically designedto achieve this end. The term "bismuth aluminate" as used herein means acoordinated complex of bismuth, oxygen, and aluminum which are notnecessarily present in the same fixed relationship for all cases coveredherein. This bismuth component can be used in any amount which iscatalytically effective, with good results obtained, on an elementalbasis, with about 0.01 to about 5 wt. % bismuth in the catalyst. Bestresults are ordinarily achieved with about 0.05 to about 1 wt. %bismuth, calculated on an elemental basis.

This bismuth component may be incorporated in the catalytic composite inany suitable manner known to the art to result in a relatively uniformdispersion of the bismuth moiety in the carrier material, such as bycoprecipitation or cogellation with the porous carrier material, ionexchange with the gelled carrier material, or impregnation with thecarrier material either after, before, or during the period when it isdried and calcined. It is to be noted that it is intended to includewithin the scope of the present invention all conventional methods forincorporating and simultaneously uniformly distributing a metalliccomponent in a catalytic composite and the particular method ofincorporation used is not deemed to be an essential feature of thepresent invention. One preferred method of incorporating the bismuthcomponent into the catalytic composite involves cogelling orcoprecipitating the bismuth component in the form of the correspondinghydrous oxide during the preparation of the preferred carrier material,alumina. This method typically involves the addition of a suitablesol-soluble bismuth compound such as bismuth trichloride, bismuthoxynitrate, and the like to the alumina hydrosol and then combining thehydrosol with a suitable gelling agent and dropping the resultingmixture into an oil bath, etc., as explained in detail hereinbefore.Alternatively, the bismuth compound can be added to the gelling agent.After drying and calcining the resulting bismuth-containing gelledcarrier material in the air, there is obtained an intimate combinationof alumina and bismuth oxide and/or bismuth aluminate. Another method ofincorporating the bismuth component into the catalytic compositeinvolves utilization of a soluble, decomposable compound or complex ofbismuth to impregnate the porous carrier material. In general, thesolvent used in this impregnation step is selected on the basis of thecapability to dissolve the desired bismuth compound without adverselyaffecting the carrier material and may be a suitable alcohol, ether,acid, and the like solvent, although it is preferably an aqueous, acidicsolution. Thus, the bismuth component may be added to the carriermaterial by commingling the latter with an aqueous acidic solution ofsuitable bismuth salt or complex of bismuth such as bismuth citrate,bismuth iodide, bismuth lactate, bismuth chloride, bismuth hydroxide,bismuth nitrate, bismuth oxynitrate, bismuth oxalate, bismuthsesquioxide, bismuth oxybromide, bismuth oxychloride, bismuthic acid,bismuth oxycarbonate, bismuth acetate, bismuth benzoate, bismuthbromide, bismuth tartrate, bismuth potassium tartrate, bismuth sodiumtartrate, bismuth ammonium citrate, and the like compounds. Aparticularly preferred impregnation solution comprises an acidicsolution of bismuth trichloride or bismuth oxynitrate in water. Suitableacids for use in the impregnation solution are: inorganic acids such ashydrochloric acid, nitric acid, and the like, and strongly acidicorganic acids such as oxalic acid, malonic acid, citric acid, and thelike. In general, the bismuth component can be impregnated either priorto, simultaneously with, or after the other ingredients are added to thecarrier material. However, good results are obtained when the bismuthcomponent is impregnated simultaneously with the platinum group andcobalt components. In fact, a preferred impregnation solution is anaqueous acidic solution of chloroplatinic acid, hydrochloric acid,bismuth trichloride, and cobaltous chloride.

A second essential ingredient of the subject catalyst is the platinumgroup component. That is, it is intended to cover the use of platinum,iridium, osmium, ruthenium, rhodium, palladium, or mixtures thereof, asa second component of the present composite. It is an essential featureof the present invention that substantially all of this platinum groupcomponent exists within the final catalytic composite in the elementalmetallic state. Generally, the amount of this component present in thefinal catalytic composite is small compared to the quantities of theother components combined therewith. In fact, the platinum groupcomponent generally will comprise about 0.01 to about 2 wt. % of thefinal catalytic composite, calculated on an elemental basis. Excellentresults are obtained when the catalyst contains about 0.05 to about 1wt. % of platinum, iridium, rhodium, or palladium metal. Particularlypreferred mixtures of these metals are platinum and iridium, andplatinum and rhodium.

This platinum group component may be incorporated in the catalyticcomposite in any suitable manner known to result in a relatively uniformdistribution of this component in the carrier material such ascoprecipitation or cogelation, ion exchange or impregnation. Thepreferred method of preparing the catalyst involves the utilization of asoluble, decomposable compound of platinum group metal to impregnate thecarrier material in a relatively uniform manner. For example, thiscomponent may be added to the support by commingling the latter with anaqueous solution of chloroplatinic or chloroiridic or chloropalladicacid. Other watersoluble compounds or complexes of platinum group metalsmay be employed in impregnation solutions and include ammoniumchloroplatinate, bromoplatinic acid, platinum trichloride, platinumtetrachloride hydrate, platinum dichlorocarbonyl dichloride,dinitrodiaminoplatinum, sodium tetranitroplatinate (II), palladiumchloride, palladium nitrate, palladium sulfate, diamminepalladium (II)hydroxide, tetramminepalladium (II) chloride, hexamminerhodium chloride,rhodium carbonylchloride, rhodium trichloride hydrate, rhodium nitrate,sodium hexachlororhodate (III), sodium hexanitrorhodate (III), iridiumtribromide, iridium dichloride, iridium tetrachloride, sodiumhexanitroiridate (III), potassium or sodium chloroiridate, potassiumrhodium oxalate, etc. The utilization of a platinum, iridium, rhodium,or palladium chloride compound, such as chloroplatinic, chloroiridic, orchloropalladic acid or rhodium trichloride hydrate, is preferred sinceit facilitates the incorporation of both the platinum group componentsand at least a minor quantity of the halogen component in a single step.Hydrogen chloride or the like acid is also generally added to theimpregnation solution in order to further facilitate the incorporationof the halogen component and the uniform distribution of the metalliccomponents throughout the carrier material. In addition, it is generallypreferred to impregnate the carrier material after it has been calcinedin order to minimize the risk of washing away the valuable platinum orpalladium compounds; however, in some cases it may be advantageous toimpregnate the carrier material when it is in a gelled state.

A third essential ingredient of the acidic multimetallic catalyticcomposite used in the present invention is a cobalt component. Althoughthis component may be initially incorporated into the composite in manydifferent decomposable forms which are hereinafter stated, my basicfinding is that the catalytically active state for hydrocarbonconversion with this component is the elemental metallic state.Consequently, it is a feature of my invention that substantially all ofthe catalytically available cobalt component exists in the catalyticcomposite either in the elemental metallic state or in a state which isreducible to the elemental state under dehydrocyclization conditions orin a mixture of these states. Examples of this last state are obtainedwhen the catalytically available cobalt component is initially presentin the form of cobalt oxide, hydroxide, halide, oxyhalide, and the likereducible compounds. As a corollary to this basic finding on the activestate of the catalytically available cobalt component, it follows thatthe presence of the catalytically available cobalt in form which are notreducible at dehydrocyclization conditions is to be scrupulously avoidedif the full benefits of the present invention are to be realized.Illustrative of these undesired forms are cobalt sulfide and the cobaltoxysulfur compounds such as cobalt sulfate. Best results are obtainedwhen the composite initially contains all of the catalytically availablecobalt component in the elemental metallic state or in a reducible oxidestate or in a mixture of these states. All available evidence indicatesthat the preferred preparation procedure specifically described inExample I results in a catalyst having the catalytically availablecobalt component in the elemental metal form and/or in a reducible oxideform. Based on the performance of such a catalyst, it is believed thatsubstantially all of this reducible oxide form of the cobalt componentis reduced to the elemental metallic state when a dehydrocyclizationprocess using this catalyst is started-up and lined-out atdehydrocyclization conditions. The cobalt component may be utilized inthe composite in any amount which is catalytically effective, with thepreferred amount being about 0.05 to about 5 wt. % thereof, calculatedon an elemental cobalt basis. Typically, best results are obtained withabout 0.1 to about 2.5 wt. % cobalt. It is, additionally, preferred toselect the specific amount of cobalt from within this broad weight rangeas a function of the amount of the platinum group component, on anatomic basis, as is explained hereinafter.

The cobalt component may be incorporated into the catalytic composite inany suitable manner known to those skilled in the catalyst formulationart to result in a relatively uniform distribution of the catalyticallyavailable cobalt in the carrier material such as coprecipitation,cogelation, ion exchange, impregnation, etc. In addition, it may beadded at any stage of the preparation of the composite -- either duringpreparation of the carrier material or thereafter -- since the precisemethod of incorporation used is not deemed to be critical. However, bestresults are obtained when the catalytically available cobalt componentis relatively uniformly distributed throughout the carrier material in arelatively small particle or crystallite size having a maximum dimensionof less than 100 Angstroms, and the preferred procedures are the onesthat are known to result in a composite having a relatively uniformdistribution of the catalytically available cobalt moiety in arelatively small particle size. One acceptable procedure forincorporating this component into the composite involves cogelling orcoprecipitating the cobalt component during the preparation of thepreferred carrier material, alumina. This procedure usually comprehendsthe addition of a soluble, decomposable, and reducible compound ofcobalt such as cobalt chloride, acetate or nitrate to the aluminahydrosol before it is gelled. Alternatively, the reducible compound ofcobalt can be added to the gelling agent before it is added to thehydrosol. The resulting mixture is then finished by conventionalgelling, aging, drying, and calcination steps as explained hereinbefore.One preferred way of incorporating this component is an impregnationstep wherein the porous carrier material is impregnated with a suitablecobalt-containing solution either before, during, or after the carriermaterial is calcined or oxidized. The solvent used to form theimpregnation solution may be water, alcohol, ether, or any othersuitable organic or inorganic solvent provided the solvent does notadversely interact with any of the other ingredients of the composite orinterfere with the distribution and reduction of the cobalt component.Preferred impregnation solutions are aqueous solutions of water-soluble,decomposable, and reducible cobalt compounds such as cobaltous acetate,cobaltous benzoate, cobaltous bromate, cobaltous bromide, cobaltouschlorate and perchlorate, cobaltous chloride, cobaltic chloride,cobaltous fluoride, cobaltous iodide, cobaltous nitrate, hexamminecobalt(III) chloride, hexamminecobalt (III) nitrate, triethylenediamminecobalt(III) chloride, cobaltous hexamethylenetetramine, and the likecompounds. Best results are ordinarily obtained when the impregnationsolution is an aqueous solution of cobalt chloride or acetate ornitrate. This cobalt component can be added to the carrier material,either prior to, simultaneously with, or after the other metalliccomponents are combined therewith. Best results are usually achievedwhen this component is added to a bismuth-containing carrier materialsimultaneously with the platinum group component via an acidic aqueousimpregnation solution. In fact, excellent results are obtained, asreported in the examples, with an impregnation procedure using an acidicaqueous solution comprising chloroplatinic acid, cobaltous chloride, andhydrochloric acid to impregnate a bismuth-containing alumina carriermaterial.

It is essential to incorporate a halogen component into the acidicmultimetallic catalytic composite used in the present invention.Although the precise form of the chemistry of the of the association ofthe halogen component with the carrier material is not entirely known,it is customary in the art to refer to the halogen component as beingcombined with the carrier material, or with the other ingredients of thecatalyst in the form of the halide (e.g. as the chloride). This combinedhalogen may be either fluorine, chlorine, iodine, bromine, or mixturesthereof. Of these, fluorine and, particularly, chlorine are preferredfor the purposes of the present invention. The halogen may be added tothe carrier material in any suitable manner, either during preparationof the support or before or after the addition of the other components.For example, the halogen may be added, at any stage of the preparationof the carrier material or to the calcined carrier material, as anaqueous solution of a suitable, decomposable halogen-containing compoundsuch as hydrogen fluoride, hydrogen chloride, hydrogen bromide, ammoniumchloride, etc. The halogen component or a portion thereof, may becombined with the carrier material during the impregnation of the latterwith the platinum group, cobalt, or bismuth components; for example,through the utilization of a mixture of chloroplatinic acid and hydrogenchloride. In another situation, the alumina hydrosol which is typicallyutilized to form the preferred alumina carrier material may containhalogen and thus contribute at least a portion of the halogen componentto the final composite. For the dehydrocyclization reaction, the halogenwill be typically combined with the carrier material in an amountsufficient to result in a final composite that contains about 0.1 toabout 3.5%, and preferably about 0.5 to about 1.5%, by weight ofhalogen, calculated on an elemental basis. It is to be understood thatthe specified level of halogen component in the instant catalyst can beachieved or maintained during use in the dehydrocyclization ofhydrocarbons by continuously or periodically adding to the reaction zonea decomposable halogen-containing compound such as an organic chloride(e.g. ethylene dichloride, carbon tetrachloride, t-butyl chloride) in anamount of about 1 to 100 wt. ppm. of the hydrocarbon feed, andpreferably, about 1 to 10 wt. ppm.

Regarding especially preferred amounts of the various metalliccomponents of the subject catalyst, I have found it to be an excellentpractice to specify the amounts of the cobalt component and the bismuthcomponent as a function of the amount of the platinum group component.On this basis, the amount of the cobalt component is ordinarily selectedso that the atomic ratio of cobalt to platinum group metal contained inthe composite is about 0.1:1 to about 66:1, with the preferred rangebeing about 0.4:1 to about 18:1. Similarly, the amount of the bismuthcomponent is ordinarily selected to produce a composite containing anatomic ratio of bismuth to platinum group metal of about 0.1:1 to about2:1, with the preferred range being about 0.2:1 to about 1:1.

Another significant parameter for the instant catalyst is the "totalmetals content" which is defined to be the sum of the platinum groupcomponent, the cobalt component, and the bismuth component, calculatedon an elemental basis. Good results are ordinarily obtained with thesubject catalyst when this parameter is fixed at a value of about 0.15to about 4 wt. %, with best results ordinarily achieved at a metalsloading of about 0.3 to about 3 Wt. %

Regardless of the details of how the components of the catalyst arecombined with the porous carrier material, the final catalyst generallywill be dried at a temperature of about 200° to about 600° F. for aperiod of at least about 2 to about 24 hours or more, and finallycalcined or oxidized at a temperature of about 700° F. to about 1100° F.in an air to oxygen atmosphere for a period of about 0.5 to about 10hours in order to convert substantially all of the metallic componentsto the corresponding oxide form. Because a halogen component is utilizedin the catalyst, best results are generally obtained when the halogencontent of the catalyst is adjusted during the oxidation step byincluding a halogen or a halogen-containing compound such as HCl or anHCl-producing substance in the air of oxygen atmosphere utilized. Inparticular, when the halogen component of the catalyst is chlorine, itis preferred to use a mole ratio of H₂ O to HCl of about 5:1 to about100:1 during at least a portion of the oxidation step in order to adjustthe final chlorine content of the catalyst to a range of about 0:1 toabout 3.5 wt. %. Preferably, the duration of this halogenation step isabout 1 to 5 hours.

The resultant oxidized catalytic composite is preferably subjected to asubstantially water-free reduction step prior to its use in thedehydrocylization of hydrocarbons. This step is designed to selectivelyreduce the platinum groups component to the elemental metallic state,while maintaining the bismuth component in a positive oxidation state,and to insure a uniform and finely divided dispersion of the metalliccomponents throughout the carrier material. Preferably, a substantiallypure and dry hydrogen stream (i.e. less than 20 vol. ppm. H₂ O) is usedas the reducing agent in this step. The reducing agent is contacted withthe oxidized catalyst at conditions including a reduction temperature ofabout 400° F. to about 1200° F. and a period of time of about 0.5 to 10hours effective to reduce substantially all of the platinum groupcomponent to the elemental metallic state, while maintaining the bismuthcomponent in a positive oxidation state. Quite surprisingly, it has beenfound that if this reduction step is performed with a hydrocarbon-freehydrogen stream at the temperature indicated, and if the catalyticallyavailable cobalt component is properly distributed in the carriermaterial in the oxide form and in the specified particle size, asubstantial amount of the catalytically available cobalt component willnot be reduced in this step. However, once the catalyst sees a mixtureof hydrogen and hydrocarbon (such as during the start-up and lining-outof the dehydrocyclization process using same), substantially all of thecatalytically available cobalt component is quickly reduced at thespecified reduction temperature range. This reduction treatment may beperformed in situ as part of a start-up sequence if precautions aretaken to predry the plant to a substantially water-free state and if asubstantially water-free hydrogen stream is used.

The resulting selectively reduced catalytic composite is, in accordancewith the basic concept of the present invention, preferably maintainedin a sulfur-free state both during its preparation and thereafter duringits use in the dehydrocyclization of hydrocarbons. As indicatedpreviously, the beneficial interaction of the catalytically availablecobalt component with the other ingredients of the present catalyticcomposite is contingent upon the maintenance of the cobalt moiety in ahighly dispersed, readily reducible state in the carrier material.Sulfur in the form of sulfide adversely interferes with both thedispersion and reducibility of the catalytically available cobaltcomponent and consequently it is a highly preferred practice to avoidpresulfiding the selectively reduced acidic multimetallic catalystresulting from the reduction step. Once the catalyst has been exposed tohydrocarbon for a sufficient period of time to lay down a protectivelayer of carbon or coke on the surface thereof, the sulfur sensitivityof the resulting carbon-containing composite changes rather markedly andthe presence of small amounts of sulfur can be tolerated withoutpermanently disabling the catalyst. The exposure of the freshly reducedcatalyst to sulfur can seriously damage the cobalt component thereof andconsequently, jeopardize the superior performance charactersticsassociated therewith. However, once a protective layer of carbon isestablished on the catalyst, the sulfur deactivation effect is lesspermanent and sulfur can be purged therefrom by exposure to sulfur-freehydrogen stream at a temperature of about 800° to 1100° F.

According to the present invention, the dehydrocyclizable hydrocarbon iscontacted with the instant acidic multimetallic catalyst in adehydrocyclization zone maintained at dehydrocyclization conditions.This contacting may be accomplished by using the catalyst in a fixed bedsystem, a moving bed system, a fluidized bed system, or in a batch typeoperation; however, in view of the danger of attrition losses of thevaluable catalyst and of well-known operational advantages, it ispreferred to use either a fixed bed system or a dense-phase moving bedsystem such as is shown in U.S. Pat. No. 3,725,249. It is alsocontemplated that the contacting step can be performed in the presenceof a physical mixture of particles of the catalyst of the presentinvention and particles of a conventional dual-function catalyst of theprior art. In a fixed bed system, the dehydrocyclizablehydrocarbon-containing charge stock is preheated by any suitable heatingmeans to the desired reaction temperature and then passed into adehydrocyclization zone containing a fixed bed of the acidicmultimetallic catalyst. It is, of course, understood that thedehydrocyclization zone may be one or more separate reactors withsuitable means therebetween to ensure that the desired conversiontemperature is maintained at the entrance to each reactor. It is alsoimportant to note that the reactants may be contacted with the catalystbed in either upward, downward, or radial flow fashion with the latterbeing preferred. In addition, the reactants may be in the liquid phase,a mixed liquid-vapor phase, or a vapor phase when they contact thecatalyst, with best results obtained in the vapor phase. Thedehydrocyclization system then preferably comprises a dehydrocyclizationzone containing one or more fixed beds or dense-phase moving beds of theinstant catalyst. In a multiple bed system, it is, of course, within thescope of the present invention to use the present catalyst in less thanall of the beds with a conventional dual-function catalyst being used inthe remainder of the beds. This dehydrocyclization zone may be one ormore separate reactors with suitable heating means therebetween tocompensate for the endothermic nature of the dehydrocyclization reactionthat takes place in each catalyst bed.

Although hydrogen is the preferred diluent for use in the subjectdehydrcyclization method, in some cases other art-recognized diluentsmay be advantageously utilized, either individually or in admixture withhydrogen, such as C₁ to C₅ paraffins such as methane, ethane, propane,butane and pentane; carbon dioxide, the like diluents, and mixturesthereof. Hydrogen is preferred because it serves the dual-function ofnot only lowering the partial pressure of the dehydrocyclizablehydrocarbon, but also of suppressing the formation ofhydrogen-deficient, carbonaceous deposits (commonly called coke) on thecatalytic composite. Ordinarily, hydrogen is utilized in amountssufficient to insure a hydrogen to hydrocarbon mole ratio of about 0.1:1to about 10:1, with best results obtained in the range of about 0.5:1 toabout 5:1. The hydrogen stream charged to the dehydrocyclization zonewill typically be recycle hydrogen obtained from the effluent streamfrom this zone after a suitable hydrogen separation step.

Since sulfur has a high affinity for cobalt at dehydrocyclizationconditions, I have found that best results are achieved in adehydrocyclization method using the instant acidic multimetalliccatalytic composite when the catalyst is used in a substantiallysulfur-free environment. The expression "substantially sulfur-freeenvironment" is intended to mean that the total amount (expressed asequivalent elemental sulfur) of sulfur-containing compounds, which arecapable of producing a metallic sulfide at the reaction conditions used,entering the dehydrocyclization zone containing the instant catalystfrom any source is continuously maintained at an amount equivalent toless than 10 wt. ppm. of the hydrocarbon charge stock, more preferablyless than 5 wt. ppm., and most preferably less than 1 wt. ppm. Since inthe ordinary operation of the subject dehydrocyclization method theinfluent hydrogen stream is autogenously produced, the prime source forany sulfur entering the dehydrocyclization zone is the hydrocarboncharge stock, maintaining the charge stock substantially free of sulfuris ordinarily sufficient to ensure that the environment containing thecatalyst is maintained in the substantially sulfur-free state. Morespecifically, since hydrogen is a major product of thedehydrocyclization process, ordinarily the input diluent stream requiredfor the process is obtained by recycling a portion of the hydrogen-richstream recovered from the effluent withdrawn from the dehydrocyclizationzone. In this typical situation, this recycle hydrogen stream willordinarily be substantially free of sulfur if the charge stock ismaintained free of sulfur. If autogenous hydrogen is not utilized as thediluent, then, of course, the concept of the present invention requiresthat the input diluent stream be maintained substantially sulfur-free;that is, less than 10 vol. ppm. of H₂ S, preferably less than 5 vol.ppm., and most preferably less than 1 vol. ppm.

The only other possible sources of sulfur that could interfere with theperformance of the instant catalyst are sulfur that is initiallycombined with the catalyst and/or with the plant hardware. As indicatedhereinbefore, a highly preferred feature of the present acidicmultimetallic catalyst is that it is maintained in a substantiallysulfur-free state; therefore, sulfur released from the catalyst is notusually a problem in the present process. Hardware sulfur is ordinarilynot present in a new plant; it only becomes a problem when the presentprocess is to be implemented in a plant that has seen service with asulfur-containing feed stream. In this latter case, the preferredpractice of the present invention involves an initial pretreatment ofthe sulfur-containing plant in order to remove substantially all of thedecomposable hardware sulfur therefrom. This can be easily accomplishedby any of the techniques for stripping sulfur from hardware known tothose in the art; for example, by the circulation of a substantiallysulfur-free hydrogen stream through the internals of the plant at arelatively high temperature of about 800° to about 1200° F. until the H₂S content of the effluent gas stream drops to a relatively low level --typically, less than 5 vol. ppm. and preferably less than 2 vol. ppm. Insum, the preferred sulfur-free feature of the present invention requiresthat the total amount of detrimental sulfur entering thedehydrocyclization zone containing the hereinbefore described acidicmultimetallic catalyst must be continuously maintained at asubstantially low level; specifically, the amount of sulfur must be heldto a level equivalent to less than 10 wt. ppm., and preferably less than1 wt. ppm., of the feed.

In the case where the sulfur content of the charge stock for the presentprocess is greater than the amounts previously specified, it is, ofcourse, necessary to treat the charge stock in order to remove theundesired sulfur contaminants therefrom. This is easily accomplished byusing any one of the conventional catalytic pretreatment methods such ashydrorefining, hydrotreating, hydrodesulfurization, and the like toremove substantially all sulfurous, nitrogenous, and water-yieldingcontaminants from this feed stream. Ordinarily, this involves subjectingthe sulfur-containing feed stream to contact with a suitablesulfur-resistant hydrorefining catalyst in the presence of hydrogenunder conversion conditions selected to decompose sulfur contaminantscontained therein and form hydrogen sulfide. The hydrorefining catalysttypically comprises one or more of the oxides or sulfides of thetransition metals of Groups VI and VIII of the Periodic Table. Aparticularly preferred hydrorefining catalyst comprises a combination ofa metallic component from the iron group metals of Group VII and ametallic component of the Group VI transition metals combined with asuitable porous refractory support. Particularly good results have beenobtained when the iron group component is cobalt and/or nickel and theGroup VI transition metal is molybdenum or tungsten. The preferredsupport for this type of catalyst is a refractory inorganic oxide of thetype previously mentioned. For example, good results are obtained with ahydrorefining catalyst comprising cobalt oxide and molybdenum oxidesupported on a carrier material comprising alumina and silica. Theconditions utilized in this hydrorefining step are ordinarily selectedfrom the following ranges: a temperature of about 600° to about 950° F.,a pressure of about 500 to about 5000 psig., a liquid hourly spacevelocity of about 1 to about 20 hr.⁻ ¹, and a hydrogen circulation rateof about 500 to about 10,000 standard cubic feet of hydrogen per barrelof charge. After this hydrorefining step, the hydrogen sulfide, ammonia,and water liberated therein, are then easily removed from the resultingpurified charge stock by conventional means such as a suitable strippingoperation. Specific hydrorefining conditions are selected from theranges given above as a function of the amounts and kinds of the sulfurcontaminants in the feed stream in order to produce a substantiallysulfur-free charge stock which is then charged to the process of thepresent invention.

It is also generally preferred to utilize the novel acidic multimetalliccatalytic composite in a substantially water-free environment. Essentialto the achievement of this condition in the dehydrocyclization zone isthe control of the water level present in the charge stock and thediluent stream which is being charged to the zone. Best results areordinarily obtained when the total amount of water entering theconversion zone from any source is held to a level less than 20 ppm. andpreferably less than 5 ppm. expressed as weight of equivalent water inthe charge stock. In general, this can be accomplished by carefulcontrol of the water present in the charge stock and in the diluentstream. The charge stock can be derived by using any suitable dryingmeans known to the art, such as a conventional solid adsorbent having ahigh selectivity for water, for instance, sodium or calcium crystallinealuminosilicates, silica gel, activated alumina, molecular sieves,anhydrous calcium sulfate, high surface area sodium, and the likeadsorbents. Similarly, the water content of the charge stock may beadjusted by suitable stripping operations in a fractionation column orlike device. And in some cases, a combination of adsorbent drying anddistillation drying may be used advantageously to effect almost completeremoval of water from the charge stock. In an especially preferred modeof operation, the charge stock is dried to a level corresponding to lessthan 5 wt. ppm. of H₂ O equivalent. In general, it is preferred tomaintain the diluent stream entering the hydrocarbon conversion zone ata level of about 10 vol. ppm. of water or less and most preferably about5 vol. ppm. or less. If the water level in the diluent stream is toohigh, drying of same can be conveniently accomplished by contacting thisstream with a suitable desiccant such as those mentioned above.

The dehydrocyclization conditions used in the present method include areactor pressure which is selected from the range of about 0 psig. toabout 250 psig., with the preferred pressure being about 50 psig. toabout 150 psig. In fact, it is a singular advantage of the presentinvention that it allows stable operation at lower pressure than haveheretofore been successfully utilized in dehydrocyclization system withall platinum monometallic catalysts. In other words, the acidicmulti-metallic catalyst of the present invention allows the operation ofa dehydrocyclization system to be conducted at lower pressure for aboutthe same or better catalyst cycle life before regeneration as has beenheretofore realized with conventional monometallic catalysts at higherpressure.

The temperature required for dehydrocyclization with the instantcatalyst is markedly lower than that required for a similar operationusing a high quality catalyst of the prior art. This significant anddesirable feature of the present invention is a consequence of theextraordinary activity of the acidic multimetallic catalyst of thepresent invention for the dehydrocyclization reaction. Hence, thepresent invention requires a temperature in the range of from 800° F. toabout 1100° F. and preferably about 850° F. to about 1000° F. As is wellknown to those skilled in the dehydrocyclization art, the initialselection of the temperature within this broad range is made primarilyas a function of the desired conversion level of the dehydrocyclizablehydrocarbon considering the characteristics of the charge stock and ofthe catalyst. Ordinarily, the temperature then is thereafter slowlyincreased during the run to compensate for the inevitable deactivationthat occurs to provide a relatively constant value for conversion.Therefore, it is a feature of the present invention that not only is theinitial temperature requirement substantially lower, but also the rateat which the temperature is increased in order to maintain a constantconversion level is substantially lower for the catalyst of the presentinvention than for an equivalent operation with a high qualitydehydrocyclization catalyst which is manufactured in exactly the samemanner as the catalyst of the present invention except for the inclusionof the cobalt and bismuth components. Moreover, for the catalyst of thepresent invention, the aromatic yield loss for a given temperatureincrease is substantially lower than for a high qualitydehydrocyclization catalyst of the prior art.

The liquid hourly space velocity (LHSV) used in the instantdehydrocyclization method is selected from the range of about 0.1 toabout 5 hr.⁻ ¹, with a value in the range of about 0.3 to about 2 hr.⁻ ¹being preferred. In fact, it is a feature of the present invention thatit allows operations to be conducted at higher LHSV than normally can bestably achieved in a dehydrocyclization process with a high qualitydehydrocyclization catalyst of the prior art. This last feature is ofimmense economic significance because it allows a dehydrocyclizationprocess to operate at the same throughput level with less catalystinventory or at greatly increased throughput level with the samecatalyst inventory than that heretofore used with conventionaldehydrocyclization catalysts at no sacrifice in catalyst life beforeregeneration.

The following working examples are given to illustrate further thepreparation of the acidic multimetallic catalytic composite used in thepresent invention and the beneficial use thereof in thedehydrocyclization of hydrocarbons. It is that the examples are intendedto be illustrative rather than restrictive.

These examples are all preferred in a laboratory scaledehydrocyclization plant comprising a reactor, a hydrogen separatingzone, heating means, cooling means, pumping means, compressing means,and the like conventional equipment. In this plant, a sulfur-free feedstream containing the dehydrocyclizable hydrocarbon is combined with ahydrogen recycle stream and the resultant mixture heated to the desiredconversion temperature, which refers herein to the temperaturemaintained at the inlet to the reactor. The heated mixture is thenpassed into contact with the instant acidic multimetallic catalyst whichis maintained in a sulfur-free and water-free equivalent and which ispresent as a fixed bed of catalyst particles in the reactor. Thepressures reported herein are recorded at the outlet from the reactor.An effluent stream is withdrawn from the reactor, cooled, and passedinto the hydrogen-separating zone wherein a hydrogen-containing gasphase separates from a hydrocarbon-rich liquid phase containing aromatichydrocarbons, unconverted dehydrocyclizable hydrocarbons, andby-products of the dehydrocyclization reaction. A portion of thehydrogen-containing gas phase is recovered as excess recycle gas and theremaining portion is passed through a high surface area sodium scrubberand the resulting substantially water-free and sulfur-free hydrogenstream is recycled through suitable compressing means to the heatingzone as described above. The hydrocarbon-rich liquid phase from theseparating zone is withdrawn therefrom and subjected to analysis todetermine conversion and selectivity for the desired aromatichydrocarbon as will be indicated in the Examples. Conversion numbers ofthe dehydrocyclizable hydrocarbon reported herein are all calculated onthe basis of disappearance of the dehydrocyclizable hydrocarbon and areexpressed in weight percent. Similarly, selectivity numbers are reportedon the basis of weight of desired aromatic hydrocarbon produced per 100weight parts of dehydrocyclizable hydrocarbon charged.

All of the catalysts utilized in these examples are prepared accordingto the following general method with suitable modification instoichiometry to achieve the compositions reported in each example.First, a bismuth-containing alumina carrier material comprising 1/16inch spheres having an apparent bulk density of about 0.5 g/cc isprepared by: forming an aluminum hydroxy chloride sol by dissolvingsubstantially pure aluminum pellets in a hydrochloric acid solution,admixing bismuth trichloride with the resulting sol in an amountsufficient to result in a finished catalyst having the hereinafterspecified amount of bismuth, adding hexamethylenetetramine to theresulting bismuth-containing alumina sol, gelling the resulting solutionby dropping it into an oil bath to form spherical particles of abismuth-containing alumina hydrogel; aging, and washing the resultingparticles with an ammoniacal solution and finally drying and calciningthe aged and washed particles to form spherical particles ofgamma-alumina containing about 0.3 wt. % combined chloride and a uniformdispersion of the required amount of bismuth in the form of bismuthoxide and/or aluminate. Additional details as to this method ofpreparing this alumina carrier material are given in the teachings ofU.S. Pat. No. 2,620,314.

The resulting bismuth-containing gamma-alumina particles are thencontacted at suitable impregnation conditions with an aqueousimpregnation solution containing chloroplatinic acid, cobaltous chlorineand hydrogen chloride. The amounts of metallic reagents contained inthis impregnation solution are carefully adjusted to yield a finalmultimetallic catalytic composite containing a uniform dispersion of thedesired amounts of platinum and cobalt. The hydrochloric acid isutilized in an amount of about 3 wt. % of the alumina particles. Inorder to ensure a uniform dispersion of the metal moieties in thecarrier material, the impregnation solution is maintained in contactwith the carrier material particles for about 1/2 to about 3 hours at atemperature of about 70° F. with constant agitation. The impregnatedspheres are then dried at a temperature of about 225° F. for about anhour and thereafter calcined or oxidized with a sulfur-free dry airstream at a temperature of about 930° F. and a GHSV of about 500 hr.⁻ ¹for about 1/2 hour effective to convert substantially all of themetallic components to the corresponding oxide forms. In general, it isa good practice to thereafter treat the resulting oxidized particleswith a sulfur-free air stream containing H₂ O and HCl in a mole ratio ofabout 30:1 at a temperature of about 930° F. for an additional period ofabout 2 hours in order to adjust the combined chloride contained in thecatalyst to a value of about 1 wt. %. The halogen-treated spheres arenext subjected to a second oxidation step with a dry sulfur-free airstream at 930° F. and a GHSV of 500 hr.⁻ ¹ for an additional period ofabout 1/2 hour. The resulting oxidized and halogen-treated particles arethereafter subjected to a dry prereduction treatment designed, aspointed out hereinbefore, to reduce substantially all of the platinumcomponent to the elemental metallic state, while maintainingsubstantially all of the bismuth component in a positive oxidationstate. This step involves contacting the catalyst particles with asubstantially suflur-free and hydrocarbon-free hydrogen streamcontaining less than 5 vol. ppm. of H₂ O at a temperature of 930° F..atmospheric pressure and a GHSV of about 400 hr.⁻ ¹ for a period ofabout 1 hour.

EXAMPLE I

The reactor is loaded with 100 cc of an acidic catalyst containing, onan elemental basis, 0.3 wt. % platinum, 1.0 wt. % cobalt, and 0.2 wt. %bismuth, and about 1 wt. % chloride. This corresponds to an atomic ratioof cobalt to platinum of 11:1 and of bismuth to platimum of 0.62:1. Thefeed stream utilized is commercial grade n-hexane. The feed stream iscontacted with the catalyst at a temperature of 920° F., a pressure of125 psig., a liquid hourly space velocity of 0.75 hr.⁻ ¹, and ahydrogen-containing recycle gas to hydrocarbon mole ratio of 4:1. Thedehydrocyclization plant is lined-out at these conditions and a 20 hourtest period commenced. The hydrocarbon product stream from the plant iscontinuously analyzed by GLC (gas liquid chromatography) and about a 90%conversion of n-hexene is observed with a selectivity for benzene ofabout 25%.

EXAMPLE II

The acidic catalyst contains, on an elemental basis, 0.375 wt. %platinum, 0.5 wt. % cobalt, 0.1 wt. % bismuth and about 1 wt. % combinedchloride. For this catalyst, the pertinent atomic ratios are: cobalt toplatinum = 4.41:1 and bismuth to platinum = 0.25:1. The feed stream iscommercial grade normal heptane. The dehydrocyclization reactor isoperated at a temperature of 900° F., a pressure of 125 psig., a liquidhourly space velocity of 0.75 hr.⁻ ¹, and a recycle gas to hydrocarbonmole ratio of 5:1. After a line-out period, a 20 hour test period isperformed during which the average conversion of the n-heptane ismaintained at about 95% with a selectivity for aromatics (a mixture oftoluene and benzene) of about 45%.

EXAMPLE III

The acidic catalyst is the same as utilized in Example II. The feedstream is normal octane. The conditions utilized are a temperature of880° F., a pressure of 125 psig., a liquid hourly space velocity of 0.75hr.⁻ ¹, and a recycle gas to hydrocarbon mole ratio of 4:1. After aline-out period, a 20 hour test shows an average conversion of about100% and a selectivity for aromatics of about 50%.

EXAMPLE IV

The acidic catalyst contains, on an elemental basis, 0.6 wt. % platinum,1.0 wt. % cobalt, 0.3 wt. % bismuth and about 1 wt. % combined chloride.On an atomic basis, the ratio of cobalt to platinum is 5.52:1 and theratio of bismuth to platinum is 0.47:1. The feed stream is a 50/50mixture of n-hexane and n-heptane. The conditions utilized are atemperature of 945° F., a pressure of 125 psig., a liquid hourly spacevelocity of 0.75 hr.⁻ ¹, and a recycle gas to hydrocarbon mole ratio of5:1. After a line-out period, a 20 hour test is performed with aconversion of about 100% and a selectively for aromatics of about 45%.The selectivity for benzene and toluene are about 20% and 25%,respectively.

It is intended to cover by the following claims, all changes andmodifications of the above disclosure of the present invention whichwould be self-evident to a man of ordinary skill in thecatalyst-formulation art or in the hydrocarbon dehydrocyclization art.

I claim as my invention:
 1. A method for dehydrocyclizing adehydrocyclizable hydrocarbon comprising contacting the hydrocarbon atdehydrocyclization conditions with an acidic catalytic compositecomprising a porous carrier material containing, on an elemental basis,about 0.01 to about 2 wt. % platinum group metal, about 0.05 to about 5wt. % cobalt, about 0.01 to about 5 wt. % bismuth and about 0.1 to about3.5 wt. % halogen; wherein the platinum group metal, catalyticallyavailable cobalt and bismuth are uniformly dispersed throughout theporous carrier material; wherein substantially all of the platinum groupmetal is present in the elemental metallic state; and whereinsubstantially all of the catalytically available cobalt is present inthe elemental metallic state or in a state which is reducible to theelemental metallic state under dehydrocyclization conditions or in amixture of these states.
 2. A method as defined in claim 1 wherein thedehydrocyclizable hydrocarbon is admixed with hydrogen when it contactsthe catalytic composite.
 3. A method as defined in claim 1 wherein theplatinum group metal is platinum.
 4. A method as defined in claim 1wherein the platinum group metal is palladium.
 5. A method as defined inclaim 1 wherein the platinum group metal is iridium.
 6. A method asdefined in claim 1 wherein the platinum group metal is rhodium.
 7. Amethod as defined in claim 1 wherein the porous carrier material is arefractory inorganic oxide.
 8. A method as defined in claim 7 whereinthe refractory inorganic oxide is alumina.
 9. A method as defined inclaim 1 wherein the halogen is combined chloride.
 10. A method asdefined in claim 1 wherein the dehydrocyclizable hydrocarbon is analiphatic hydrocarbon containing 6 to 20 carbon atoms per molecule. 11.A method as defined in claim 10 wherein the aliphatic hydrocarbon is anolefin.
 12. A method as defined in claim 10 wherein the aliphatichydrocarbon is a paraffin.
 13. A method as defined in claim 12 whereinthe paraffin hydrocarbon is a paraffin containing 6 to 10 carbon atomsper molecule.
 14. A method as defined in claim 12 wherein the paraffinis hexane.
 15. A method as defined in claim 12 wherein the paraffin isheptane.
 16. A method as defined in claim 12 wherein the paraffin isoctane.
 17. A method as defined in claim 12 wherein the paraffin isnonane.
 18. A method as defined in claim 12 wherein the paraffin is amixture of C₆ to C₉ paraffins.
 19. A method as defined in claim 1wherein the dehydrocyclizable hydrocarbon is contained in a naphthafraction boiling in the range of about 140° F. to about 400° F.
 20. Amethod as defined in claim 2 wherein the dehydrocyclization conditionsinclude a temperature of 800° to about 1100° F., a pressure of 0 to 250psig, a LHSV of 0.1 to 5 hr.⁻ ¹, and a hydrogen to hydrocarbon moleratio of about 0.1:1 to about 10:1.
 21. A method as defined in claim 1wherein the acidic catalytic composite contains, on an elemental basis,about 0.05 to about 1 wt. % platinum group metal, about 0.1 to about 2.5wt. % cobalt and about 0.05 to about 1 wt. % bismuth and about 0.5 toabout 1.5 wt. % halogen.
 22. A method as defined in claim 1 wherein themetals content of the catalytic composite is adjusted so that the atomicratio of bismuth to platinum group metal is about 0.1:1 to about 2:1.23. A method as defined in claim 1 wherein the metals content of thecatalytic composite is adjusted so that the atomic ratio of cobalt toplatinum group metal is about 0.1:1 to about 66:1.
 24. A method asdefined in claim 1 wherein the contacting is performed in asubstantially water-free environment.
 25. A method as defined in claim 1wherein the contacting is performed in a substantially sulfur-freeenvironment.
 26. A method as defined in claim 1 wherein substantiallyall of the catalytically available cobalt contained in the composite ispresent in the elemental metallic state after the method is started-upand lined-out at dehydrocyclization conditions.
 27. A method as definedin claim 1 wherein substantially all of the bismuth is present in thecatalytic composite in an oxidation state above that of the elementalmetal.
 28. A method as defined in claim 27 wherein substantially all ofthe bismuth is present in the catalytic composite as bismuth oxide orbismuth aluminate.
 29. A method as defined in claim 1 wherein thecatalytic composite is in a sulfur-free state.